WifiStack: Fix build error occurred by not allowed artifact path

WifiRRROverlaySampleApp.apk has to be in system/* instead of product/*
because of mainline_system.mk

Bug: 151693586
Test: Verified that the sample overlay app can override configs.
(cherry-picked from go/pag/1604758)

Change-Id: Ia0232e4f6e976a53302d62c985a3d1c34b0f5a8a
1 file changed